2. The acoustic model of the pump was also used to determine the
ideal sound sources that generate acoustic fields equivalent to
the sound emission by fluid-dynamic blade–tongue interaction
at different flow-rates. For flow-rates below nominal, the ideal
sources identified were two monopoles closely located at the
tongue region of the volute that approximately behave like a
dipole. For nominal and high flow rates, the ideal sources are
two dipoles also located at the tongue region of the volute,
which behave approximately as a lineal quadrupole.
3. The effect of the acoustic pump-circuit coupling was studied
both theoretically and experimentally, with particular attention
on the influence of the acoustic characteristics at the suction
side of a laboratory pump on the pressure fluctuations at the
blade-passing frequency. Tests showed that when the centrifugal
pump was run at 1620 rpm, the change of the acoustic
impedance of the suction side by opening a closed side branch,
which led to a dead end (with no mean flow through it), had
almost no influence on the pressure fluctuations at the tongue
region of the pump. In contrast, a significant difference in the
pressure fluctuations at the tongue region was found when
closing that same valve at 2040 rpm. In fact, the fBP associated
to this speed was predicted by the pump-circuit acoustic model
as a resonance frequency of the system depending on valve V4.
This last result suggests that although significant blade-passing
frequency noise may be generated when a pump is operating well
off nominal conditions, the impact of this noise could be reduced
by proper design of the associated piping in order to avoid strong
acoustic feedback.
2. The acoustic model of the pump was also used to determine theideal sound sources that generate acoustic fields equivalent tothe sound emission by fluid-dynamic blade–tongue interactionat different flow-rates. For flow-rates below nominal, the idealsources identified were two monopoles closely located at thetongue region of the volute that approximately behave like adipole. For nominal and high flow rates, the ideal sources aretwo dipoles also located at the tongue region of the volute,which behave approximately as a lineal quadrupole.3. The effect of the acoustic pump-circuit coupling was studiedboth theoretically and experimentally, with particular attentionon the influence of the acoustic characteristics at the suctionside of a laboratory pump on the pressure fluctuations at theblade-passing frequency. Tests showed that when the centrifugalpump was run at 1620 rpm, the change of the acousticimpedance of the suction side by opening a closed side branch,which led to a dead end (with no mean flow through it), hadalmost no influence on the pressure fluctuations at the tongueregion of the pump. In contrast, a significant difference in thepressure fluctuations at the tongue region was found whenclosing that same valve at 2040 rpm. In fact, the fBP associatedto this speed was predicted by the pump-circuit acoustic modelas a resonance frequency of the system depending on valve V4.This last result suggests that although significant blade-passingfrequency noise may be generated when a pump is operating welloff nominal conditions, the impact of this noise could be reducedby proper design of the associated piping in order to avoid strongacoustic feedback.
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